3000 



■o 2500 



c 



S 2000 



I 1500 - 



1 



- 1000 



o 500 







Annual Mean Streamflow (Cfs) 



Long-term mean 



I 



llllllllJllj 



1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 



Figure 10. Annual mean discharge for calendar years 1988-3003. 



Results/Discussion 



Results Part I: Blackfoot River Environment 



Blackfoot River Discharge: USGS Bonner gauging station #12340000 



By 2002 

 and 2003, the 

 Blackfoot River 

 watershed was 



subject to a third 

 and fourth year of 

 consecutive 

 drought. Mean 



discharge was 



1501 cfs in 2002 

 and 1330 cfs in 

 2003, compared 

 with a long-term 

 mean of 1596 cfs 

 (Figure 10). 



The relative 

 drought index for 

 the Blackfoot 



River at Bonner 

 showed daily river 

 discharge at <75% 

 of mean monthly 

 flow on 135 days 

 for 2002 and 196 

 days for 2003, with 

 daily river 



discharge <50% of 

 monthly mean on 

 16 and 23 days 

 respectively 

 (Figure 1 1 ). For 

 the calendar year 



Number of Days Stream Discharge 



300 



260 



200 



150 



100 



1988 -90 



'95 



■00 



2003 



Figure 11. Relative drought index near Bonner: number of days river 

 discharge was < 50% and < 75% of monthly mean for calendar years 1988- 

 2003 



2002, flows were particularly low during late winter and early spring with daily flows 

 <75% of mean monthly for 77 of 121-day period between February and May. During 



2003, winter flows approached normal although non-winter flows (May-October) were 

 very low, falling to <75% of mean monthly flows on 149 of 184 days. 



27 



